Internal combustion engine with an exhaust emission control system

ABSTRACT

The invention relates to an internal combustion engine with an exhaust emission control system which comprises at least one catalyst, with the exhaust gas flow being reversible by the catalyst. A first installation position is provided for a first lambda sensor upstream of the catalyst and a second installation position for a second lambda sensor downstream of the catalyst, with the first and second installation positions being arranged symmetrically relative to the transversal plane.

FIELD OF THE INVENTION

The invention relates to an internal combustion engine with an exhaust emission control system which comprises at least one catalyst, with the exhaust gas flow being reversible by the catalyst.

BACKGROUND OF THE INVENTION

Catalysts of exhaust emission control systems are subjected to an ageing process during long service life of the internal combustion engine. Said ageing process causes an increasing deterioration in the emission values, as a result of which an expensive exchange of catalysts is required in many cases.

DE 196 40 604 A1 discloses a method for reactivating/regenerating exhaust gas catalysts. The early recycling of the catalyst is avoided by reversing the direction of flow by means of turning, by separating the deactivated part or by deflecting the main gas stream to the as yet not deactivated ducts on the outside of the catalyst.

DE 43 01 286 A1 describes a catalyst element for a ship propulsion apparatus which can be reoriented from a first orientation to a second orientation differing from the first orientation. It is thus ensured that deposited residues are blown away from the catalyst element again once the same has been reoriented in such a way that the side formerly facing the exhaust inlet now faces the exhaust outlet. The life of the catalyst element is thus extended.

U.S. Pat. No. 3,072,457 A shows an arrangement with two catalysts, in which the direction of flow of the exhaust gas is reversed by the catalysts by means of a valve. The reversal of the direction of flow occurs in certain time intervals.

DE 198 35 565 A1 describes an apparatus for the aftertreatment of exhaust gases of a diesel engine, comprising a monolith which is flowed through by exhaust gas and which is arranged rotatably in the exhaust gas stream. By turning the monolith an excessive enrichment of the particles is avoided. Moreover, counted regeneration measures for the monolith can be initiated through free controllability of the rotation.

SUMMARY OF THE INVENTION

It is the object of the invention to avoid this disadvantage and to extend the service life of a catalyst in an exhaust emission control system.

This is achieved in accordance with the invention in such a way that a first installation position is provided for a first lambda sensor upstream of the catalyst and a second installation position for a second lambda sensor downstream of the catalyst, with the first and second installation positions being arranged symmetrically relative to the transversal plane, with preferably the installation positions having identical screw threads for the lambda sensors. The invention makes use of the fact that the first region of the catalyst which is subject to the highest temperature peaks is subjected to the strongest ageing, whereas areas of the catalyst which are situated downstream of said ageing-susceptible area are not subject to any ageing or only to very little thereof. By reversing the direction of flow of the catalyst, the conversion rate could thus be increased again and thus the quality of the exhaust gas be improved without requiring a renewal of the catalyst.

Ageing of the catalyst causes the first part of the catalyst to become inactive. This leads to a delayed activation of the catalyst (increased light-off temperature) after cold starting because although the first part of the catalyst absorbs heat, it does not contribute to the conversion of pollutants. After the turning of the catalyst, the most forward part of the catalyst is active again. The light-off temperature decreases again.

It is preferably provided that the catalyst is turned after a defined operating period of the internal combustion engine or after a certain mileage, with preferably the catalyst being removed and, after being turned about 180°, being installed again into the emission control system in reversed direction of flow. This enables a high service life of the catalyst. These measures could be performed for example within the scope of a regular engine service in a workshop. The precondition is that the catalyst is arranged so as to have a reversible configuration, with preferably the catalyst being arranged symmetrically with respect to a transversal plane which is arranged normally to the direction of flow.

Emission control systems with catalysts usually have installation positions for lambda sensors upstream and downstream of the catalyst. The sensor upstream of the catalyst is the control sensor and the sensor downstream of the catalyst is the diagnostic sensor. The turning of the catalyst is substantially simplified when the first and the second installation position are arranged symmetrically with respect to the transversal plane, with preferably the installation positions having identical screw threads for the lambda sensors. The lambda sensors can be arranged in the exhaust pipe before or after the catalyst or in the cone before or after the catalyst.

The invention is now explained in closer detail by reference to the drawing.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE Shows schematically an internal combustion engine according to the present invention.

DETAILED DESCRIPTION OF THE DRAWING

The drawing schematically shows an internal combustion engine 1 with an exhaust gas system 2 in which an emission control system 3 with a catalyst 4 is arranged. The catalyst 4 is arranged symmetrically with respect to a transversal plane ε which is arranged normal to the direction of flow S. Moreover, the installation positions 5, 6 for lambda sensors (not shown in closer detail) which are provided in the inlet and outlet cone 7, 8 of catalyst 4 are arranged upstream and downstream of catalyst 4 in a symmetrical way with respect to the transversal plane ε. The screw threads for the lambda sensors are also arranged identically, so that in the case of a reversed installation of catalyst 4 the lambda sensors can be changed, with the function of the upstream lambda sensor as a control probe and the downstream lambda sensor as a diagnostic sensor being maintained. This ensures that the catalyst 4 can be installed in the exhaust system 2 irrespective of the direction of flow S of the exhaust gases.

After a defined mileage of 100,000 km for example, the catalyst 4 is removed from the exhaust train and installed again after having been turned by 180°. This measure ensures that the exhaust gas from the internal combustion engine 1 passes at first through the inlet regions 4 a of the catalyst which until now have not been subject to thermal ageing or to only very little thereof, whereas strongly aged regions 4 b are arranged in the area of the catalyst outlet. By turning the catalyst 4 in the exhaust system 2, the conversion rate of the catalyst 4 can be improved considerably and the quality of the emissions can be improved decisively without renewing catalyst 4.

The measure of the turned installation of a symmetrically arranged catalyst 4 can also be applied when using used exchange catalysts which are installed in a direction of flow which is reversed over the prior one and thus forms a cost-effective possibility in order to extend the service life of internal combustion engine 1 by maintaining statutory emission requirements without using a new catalyst. 

1. An internal combustion engine with an exhaust emission control system which comprises at least one catalyst, with an exhaust gas flow being reversible by the catalyst, wherein a first installation position is provided for a first lambda sensor upstream of the catalyst and a second installation position for a second lambda sensor downstream of the catalyst, with the first and second installation positions being arranged symmetrically relative to a transversal plane.
 2. An internal combustion engine according to claim 1, wherein the installation positions have identical screw threads for the lambda sensors.
 3. An internal combustion engine according to claim 1, wherein the catalyst is arranged symmetrically with respect to a transversal plane which is arranged normally to the direction of flow. 